That led to a solution if not clarity, thanks!
You can check the log here: https://pastebin.com/ygxFfheW
It seems it is related to X11<->Wayland weirdness, with a: GLib-GObject-WARNING **: 23:37:19.071: invalid cast from 'GdkWaylandDisplay' to 'GdkX11Display'
A quick search turned up a the same solution as wunderseltsam mentioned above; instead of running the file from the file browser, if 1BitDragon is launched with the following command the save/load works as expected under a Wayland session.
Use as mentioned above:
$ GDK_BACKEND=x11 ./1BITDRAGON.x86_64